Almost all public buildings are required to have signs identifying emergency exits. These signs are generally rectangles and are perhaps 12 inches long and eight inches high. The dimensions may vary depending on the code or standard governing the size of the signs.
Most of these signs are illuminated by incandescent lamps. In order to illuminate the entire sign, two 20-watt lamps are usually required. Most fire codes require that the signs be lit continuously while the building is occupied. Since many public buildings have numerous exits, a single building may have lieterally hundreds of signs consuming thousands of kilowatts of electricity per year. In addition, the signs generate heat which must be removed during the air conditioning season. Since the signs are located near ceilings, the heat input during the heating season is minimized because the heat input therefrom is conducted and convected along the floors to the exterior walls of the building. Moreover, at least one of the emergency exit lightbulbs can be expected to burn out during the course of the year. When a building has hundreds of emergency exit signs, the cost of replacing these bulbs can be quite high. When one consdiers the cost of the bulbs themselves, they are expensive (as is the cost of the labor required to replace the bulb). One inventor who has studied this problem, Emanuel L. Logan, Jr., estimates that each emergency exit sign costs between $70 and $ 120 per year to operate and maintain.
In view of these considerations, a new type of emergency exit sign which is inexpensive to operate and maintain is needed.